My friend Jon and I did some practice work on braze-ons with three techniques.
The first approach was Jon’s traditional flux brazing followed by cleanup and some file work. Very little heat stress with this technique.
I also did one with TIG and silicon bronze. Si-Bronze goes about as quick as normal TIG but it does not generally look as good. The advantage with Si-Bronze TIG is that heat input is much lower so it does not stress the tube as much as normal TIG.
For comparison, I did one with TIG and normal steel filler rod. Steel TIG goes fast and does not require any post weld cleanup time. I prefer using Si Bronze because it puts less heat stress on the tubing.
The one we did with flux brazing looks the best (thanks Jon). Flux brazing is also the best at sealing up the area inside the braze-on but it requires quite a bit of clean up. For reference the following photo is the flux before final cleanup. I actually ran a wire wheel on the braze on but that was not enough. To really clean up flux you need to soak in hot water and do some file work.
There are many builders who use each of these techniques. Personally I like the look of flux brazing for road bikes and show bikes but on a work-a-day mountain bike using TIG makes sense because it is much less effort.
The Si Bronze looks good!
braze on are called braze-ons for a reason….weld on are weld ons…TIG is a PITA for brazeons and if you are halfway good at it you need no post cleanup other than soaking off the flux which takes 1 minute. IMHO other than weld-ons for Titinium , TIG welding your braze-ons is atrocious and degrades the mechanical properties of most steels while creating stress risers.
Ya, I will agree with you that on super thin steels traditional brazing is better but lots of framebuilders do TIG brazons and they work well in most applications. Steve Garn had used TIG for brazons on thousands of frames and feels it is a good and robust technique if done properly.
I use his approach of doing TIG with Si Bronze wire. In this case it is actually TIG brazing because the base steel of the frame never melts and the brazon is mounted only with the Si Bronze at much lower amps then TIG welding.